thats part of the argument for algos,shortly there will be alternate exchanges,however i believe it will all still pass through these exchanges thats part of the revisions that supposedly prevent large firms creating their own exchanges--that would be the dark pools.
some stocks are very tightly held by platforms,and are very difficult to trade--large high volume stocks have algos living in them,soreads are generally appalling.
these days i sit in a fund that actively trades,of course should i think there is better opportunity elsewhere i will move houses
